This invention relates to a solder reflow oven, and in particular to such an oven suitable for reflowing solder balls placed on solder pads of a ball grid array (BGA) substrate. The invention also relates to a compact and advantageous system for solder ball attachment in BGA electronic packages.
A ball grid array (BGA) is a well-known and increasingly popular form of electronic package design for the use in the manufacture of integrated circuits. One of the important steps in the manufacturing process for a BGA is the firm attachment of solder balls onto solder pads formed on a BGA substrate. The solder ball is used to maintain electrical connectivity between the BGA substrate and any components attached thereto. The attachment of the solder balls to the solder pads involves two main steps: (1) solder ball placement, and (2) solder reflow. The first step involves the picking of a number of solder balls from a supply means by a pick head, and then the placement of those balls in a desired pattern on the BGA substrate such that one solder ball is placed on each solder pad. The second process involves the solder balls being melted and reflowed on the solder pads of the substrate. The present invention is concerned in particular with this second step.
The solder reflow step involves four well-defined phases: preheat, soak, reflow (spike) and cooling. Firstly, in the preheat phase the solder balls are warmed to a temperature that is just below the melting point of the solder. For example the balls may be heated to about 30xc2x0 C. below a melting point of 183xc2x0 C. In the soak phase, the flux that is used to adhere the solder balls to the solder pads is activated to remove oxide on the pads, and the temperature of the substrate and the solder balls are allowed to become more uniform and stabilized. During this soak period the temperature of the solder balls and the substrate is nearly constant or may increase slightly, for example by about 20xc2x0 C. In the reflow or spike period the temperature is caused to increase rapidly, and exceed the melting point by between 20xc2x0 C. and 50xc2x0 C. such that the solder balls will melt and wet the solder pads. Finally, in the cooling phase the solder balls and the substrate are allowed to cool to a temperature well below the melting point of the solder such that the solder balls solidify and the reflow process is complete.
The solder ball reflow process is analogous to the solder reflow of electronic components onto a printed circuit board (PCB) for which many types of reflow oven have been developed. Conventionally such PCB reflow ovens have been used for carrying out solder ball reflow. However, PCB reflow is a more complex operation that requires as a result an oven that is larger, more complex and more expensive than might be necessary for solder ball reflow alone. Furthermore it is not generally possible, or at least is not easy, to incorporate a PCB reflow oven being used as a solder reflow oven into the small compact and convenient BGA manufacturing process. There is therefore a need for a small, simple and relatively low-cost solder reflow oven that can easily be incorporated into a BGA manufacturing process.
According to the present invention there is provided a solder reflow oven for the processing of components bearing solder, comprising: input means for introducing components into said oven, a processing chamber within which said components are subject to a solder reflow process, and output means for discharging components from said oven for further processing or handling, and means for transferring said components through said processing chamber in a first direction towards said output means, wherein said processing chamber comprises a plurality of heating and cooling zones arranged with a constant pitch in the first direction, and wherein said transferring means is adapted to move said components in said first direction in stages, with each component moving a distance equal to the pitch between two zones in each stage, whereby the components are moved from zone to zone in stages.
According to another aspect of the present invention there is provided a solder reflow oven for the processing of components bearing solder, comprising: input means for introducing components into said oven, a processing chamber within which said components are subject to a solder reflow process, and output means for discharging components from said oven for further processing or handling, and means for transferring said components through said processing chamber in a first direction towards said output means, wherein said processing chamber comprises a plurality of heating and cooling zones, wherein each said block of each said heating zone and each said block of each said cooling zone is connected to a source of fresh gas, wherein each block of each said heating zone is provided with means for heating said gas, and each block of each said cooling zone is provided with means for cooling said gas, and wherein each block is formed with a serpentine channel between said source of fresh gas and at least one opening through which said gas is discharged from said block towards a component.